Dynamic characteristic analysis of a twin-spool rotor-casing system with looseness and intershaft rubbing coupling faults

Severe looseness and unbalance of a twin-spool rotor system aggravate the vibration of the entire system, which may induce secondary faults such as intershaft rubbing. To address this issue, the dynamic responses of a twin-spool rotor-casing system with looseness and intershaft rubbing coupling faults are analyzed. First, considering nonlinear factors, such as looseness and intershaft rubbing force, the governing equations of the twin-spool rotor-casing system are derived based on the finite element discretization method. To deal with second-order nonlinear differential equation, a modified Newmark-beta method based on Gaussian elimination is proposed. On this basis, the effects of looseness and intershaft rubbing fault on the dynamic responses of the rotor system are discussed through numerical simulations. Results indicate looseness fault increases the vibration of the rotor system. As the support stiffness decreases, the rotational orbit becomes irregular and complex, and the displacement in the vertical direction varies remarkably. Moreover, looseness can cause the rotor system to induce the secondary intershaft rubbing fault. Compared with the rotor system without looseness, the rotational speed corresponding to the first intershaft rubbing drops due to the effect of looseness. As the initial intershaft clearance grows, most of partial rubbing states evolve into no rubbing, and the possibility of intershaft rubbing decreases.